package cn.edu.scau.cmi.suwenpeng.chapter06;

abstract class A6_9 {
	abstract int sum(int x, int y);

	int sub(int x, int y) {
		return x - y;
	}
}

class B6_9 extends A6_9 {
	int sum(int x, int y) {
		return x + y;
	}
}

public class Example6_9 {

	public static void main(String[] args) {

		B6_9 b=new B6_9();
		int sum=b.sum(30, 20);
		int sub=b.sub(30, 20);
		System.out.println("sum="+sum);
		System.out.println("sub="+sub);
	}

}
